Moral Absolutism is the ethical belief that there are absolute standards against which moral questions can be judged, and that certain actions are right or wrong, regardless of the context of the act. Thus, actions are inherently moral or immoral, regardless of the beliefs and goals of the individual, society or culture that engages in the actions. It holds that morals are inherent in the laws of the universe, the nature of humanity, the will of God or some other fundamental source.

It is the opposite of Moral Relativism, the position that moral propositions do not reflect objective and/or universal moral truths, but instead make claims relative to social, cultural, historical or personal circumstances. It is related to, but not the same as, Moral Realism (the position that certain acts are objectively right or wrong, independent of human opinion), and to Moral Universalism (the position that there is a universal ethic which applies to all people, regardless of culture, race, sex, religion, nationality, sexuality or other distinguishing feature).

The ancient Greek philosophers Plato and Aristotle believed in a kind of Absolutism or Universalism, opposing the Moral Relativism of the Sophists. Immanuel Kant was a prominent promoter of Moral Absolutism, and his formulation of the deontological theory of the Categorical Imperative was essentially absolutist in nature. Moral Absolutism has been favoured historically largely because it makes the creation of laws and the upholding of the judicial system much simpler, and manifested itself in outdated concepts such as the Divine Right of Kings.

Many religions have morally absolutist positions, and regard their system of morality as having been set by a deity, and therefore absolute, perfect and unchangeable. Many Christians regard Christian theology as teaching a hierarchy of moral absolutes known as graded absolutism, where in the case of a conflict between two absolutes, the duty to obey the higher one (God) exempts one from the duty to the lower ones (fellow humans or, still lower, property). Divine Command Theory is an absolutist meta-ethical theory that an act is obligatory if (and only if) it is commanded by God (William of Ockham argued that if God had commanded murder, then murder would indeed have been morally obligatory).

Sometimes, Moral Absolutism can mean the more extreme position that actions are moral or immoral even regardless of the circumstances in which they occur (e.g. lying is always be immoral, even if done to promote some other good, such as to save a life). In this form, it can be contrasted with Consequentialism (in which a morally right action is one that produces a good consequence or outcome, regardless of the intentions).

A primary criticism of Moral Absolutism regards how we come to know what the absolute morals are. For morals to be truly absolute, they would have to have a universally unquestioned source, interpretation and authority, which critics claim is an impossibility.

Another of the more obvious criticisms is the sheer diversity of moral opinions which exists between societies (and even within societies) in the world today, which suggests that there cannot be a single true morality.

A Consequentialist would argue that it cannot be right for a Moral Absolutist to be unprepared to kill one man in order to prevent the deaths of many others, although this would be a rather extreme and dogmatic example of Moral Absolutism.